A drilling tool of this type is known (DE-A-42 14 528), which is adapted to be clamped in a machine spindle and comprises a drill shank provided with a feed helix delimiting a chip removal groove and a drill head disposed on the face of the drill shank. The drill head has two segment portions which are delimited radially outwardly by partially cylindrical circumferential surfaces which together form a common circumferential cylinder and which are separated from each other by chip channels which adjoin each other in a circumferential direction, which are aligned essentially axially parallel, and which merge in the chip removal groove in the chip flow direction. The drill head further has at least two cutting inserts which are disposed at different radial distances from the axis of the drill with partially overlapping working areas in an appertaining recess of the segment portions in the region of an axially parallel radial chip diverting surface, preferably with the face aligned thereto, and which have at least one active cutting edge protruding over the face of the drill head, wherein the cutting edge of the outermost cutting insert protrudes radially over the appertaining partially cylindrical circumferential surface and wherein the drill head has a larger outer diameter than the drill shank. By a specific alignment of the cutting inserts which partially overlap in the effective region of their cutting edges it is ensured that the lateral forces acting on the cutting edges during the drilling operation are essentially compensated, so that workpieces can be bored essentially without guide means. The centering is effected by means of an axially centered centering drill. The chip grooves which extend axially parallel along the drill shank and which have a triangular cross section each merge in the direction of chip flow in a relatively steep helical chip transport groove provided in the drill shank, which grooves are formed into the material of the shank. The edges of the chip removal grooves are delimited by a feed helix which serves on the one hand to guide the drill within the bore hole and on the other hand to delimited the chip removal grooves. A separate chip removal groove is assigned to each chip channel in the drill shank, into which groove the channel merges in the direction of chip flow. In this design the chips are especially pushed outwards through the chip removal grooves under the influence of a coolant. By the forming of the comparatively broad feed helix, it is attempted to prevent chips from being distributed out of the chip removal grooves over the circumference of the drill shank, which would otherwise bear the danger of the chips fusing with the bore wall and the drill shank, thus leading to a destruction of the bore and the drilling tool. A further problem exists in that the chip channel forms, in the region of the inner insert, a comparatively broad chip space having a triangular cross section, which chip space tightens toward the rear in the direction of chip flow in a funnel-like manner. This leads to the result that the chip may be formed to be relatively broad during its creation and then has to be forced into the chip removal groove with deformation work. By this a large amount of the thrust energy imparted to the chips in their creation is lost in the form of deformation work and cannot be used to aid the removal of the chips. Furthermore, the deformation forces are partially transformed into lateral forces which cause a radial deflection of the drill head and therefore a degradation of the drilling efficiency and quality. For this reason guideless drills of this type can be employed only for comparatively shallow bores up to a depth of up to 6.times.D, wherein D denotes the diameter of the bore.
Based on this it is the object of the invention to develop a drilling tool which may be used for great bore depths of 12.times.d and more, and which still guarantees an effective and almost lateral force-free chip flow.